Bug#709224: openblas: disable memory warmup

[Julian Taylor]

Package: openblas
Version: 0.2.6-2
Severity: wishlist

openblas runs some memory address range benchmarking when it starts up
to determine the fastest address range.
This is not very useful for regular non-NUMA machines and increases
startup time of applications quite significantly.

Please disable this warmup for the package so it can be used as a
general blas library replacement for all libraries.
NUMA clusters most likely build openblas themselves anyway.

It can be disabled by uncommenting NO_WARMUP in Makefile.rule

As example the import time of python numpy doubles when using openblas:

without openblas (atlas blas provider):
time python -c "import numpy"
0.8s

with warmup enabled openblas
time python -c "import numpy"
0.18s

with warmup disabled openblas
time python -c "import numpy"
0.1s